1. Field of the Invention
The invention relates to a brake with a rotating element, with a magnet wheel, which is held on the rotating element in such a way that
it rotates with the rotating element about an axis of rotation,
a first side of the magnet wheel, which lies transversely to the axis of rotation, faces the rotating element, and
a second side of the magnet wheel, which lies transversely to the axis of rotation, faces away from the rotating element, and with a first axial stop that interacts with a first stop section located on the first side of the magnet wheel and a second axial stop that interacts with a second stop section located on the second side of the magnet wheel for limiting the axial movement of the magnet wheel relative to the rotating element to a first predetermined amount.
2. Description of the Related Art
Brakes of the type referred to above are well known and are described, for example, in DE 42 30 012 C2 and EP 0 666 478 B1.
In a first embodiment described in DE 42 30 012 C2, the magnet wheel has an integrated spring, which axially pretensions the magnet wheel in the direction of the rotating element, which in this case is a brake disk. In accordance with a second embodiment, an end section of the magnet wheel is radially widened towards the outside and engages a corresponding recess in the brake disk, which likewise produces axial pretensioning of the magnet wheel in the direction of the brake disk.
In accordance with EP 0 666 478 B1, axial pretensioning of the magnet wheel against the rotating element, which in this case is also a brake disk, is achieved by providing the magnet wheel with spring-like projections that fit into grooves.
In the previously known brakes, the mount for mounting the magnet wheel on the rotating element tends to experience rust creepage. This can lead to distortion of the magnet wheel. Furthermore, it is difficult to change the magnet wheel. In addition, the previously known mounts for mounting the magnet wheel on the rotating element do not allow compensation for differences in material expansion when the brakes become hot, which means that there is the risk that the magnet wheel will fail to remain in its proper position.
The object of the invention is to refine a brake of the above-mentioned type in such a way that the risk of rust creepage is eliminated and space is available for the consequences of differences in material expansion.
In accordance with the invention, this object is met by providing that, along each line that is parallel to the axis of rotation and extends through the first or the second axial stop, the distance between the first stop section and the second stop section is smaller than the distance between the first axial stop and the second axial stop.
The invention is based on the surprisingly simple recognition that the problems arising in the state of the art are minimized, if the axial pretensioning of the magnet wheel against the rotating element is practically eliminated. In other words, in accordance with the invention, the magnet wheel is supported in a quasi-xe2x80x9cfloatingxe2x80x9d way. Specifically, since the distance between the first stop section and the second stop section is smaller than the distance between the first axial stop and the second axial stop, the magnet wheel always rests at most against one axial stop or the other, but never against both axial stops at the same time. This leads to considerable reduction or even elimination of rust creepage. Furthermore, it is self-evident that the xe2x80x9cfloatingxe2x80x9d bearing or mounting of the magnet wheel on the rotating element also tolerates differences in material expansion under the influence of heat, so that these differences in expansion do not cause distortion of the magnet wheel.
In accordance with the invention, it is preferred for the second axial stop to be formed on a separate retaining device. In this way, the magnet wheel can have a much simpler design, especially compared to the design described in EP 0 666 478 B1.
In another preferred embodiment, the first axial stop may be formed on a separate retaining device. This allows a simpler design of the rotating element. It is also not necessary for cooling vanes possibly present on the rotating element to be simultaneously used for the originally unintended purpose of retaining the magnet wheel, as is the case, for example, in the design specified in DE 42 30 012 C2.
In another preferred embodiment of the invention, the rotating element has a recess for at least partially receiving the retaining device. The formation of this type of recess on the rotating element is a very simple design measure that otherwise entails no disadvantages with respect to the construction of the rotating element.
In a preferred and especially simple development of the invention, the retaining device has a snap ring or spring ring. A snap ring or spring ring combines the advantages of especially simple installation and removal, on the one hand, and an especially high degree of reliability, on the other hand.
Additionally or alternatively, it is possible, in accordance with the invention, for the retaining device to have an anchoring device that lies parallel to the axis of rotation. This makes it especially easy to install and remove the retaining device and thus the magnet wheel, because the anchoring element needs to be moved only in the axial direction to accomplish these tasks.
A design in which the second axial stop lies at a free end of the anchoring element is preferred as an especially simple design. In other words, use is made, for example, of the principle of a screw with a screw head, such that the underside of the screw head serves as the axial stop.
To that extent, it is further preferred, in accordance with the invention, for the second axial stop to be formed in one piece with the anchoring device.
Alternatively, however, the second axial stop may also be formed on a disk penetrated by the anchoring device. In this way, especially the surface of the second axial stop can be enlarged beyond the standard size of, for example, screws, which further increases flexibility.
In accordance with an especially preferred embodiment of the invention, the first stop section is formed on an axial extension of the rotating element, which covers an angular sector about the axis of rotation of less than 360. Compared to a design with a first stop section that is closed like a ring, this decreases the stop surface, which reduces to a minimum both heat transfer from the material of the brake to the magnet wheel and the possibility of incipient rusting. Furthermore, lateral surfaces of the axial extension that are directed in the peripheral direction may serve the purpose of rotational coupling with the magnet wheel.
In another preferred embodiment of the invention, the brake has a radial stop that interacts with a third stop section of a peripheral surface of the magnet wheel for limiting movement of the magnet wheel relative to the rotating element in a direction transverse to the axis of rotation to a second predetermined amount, which is greater than zero.
In other words, in this embodiment of the invention, the magnet wheel is supported in a quasi-xe2x80x9cfloatingxe2x80x9d way not only in the axial direction, but also in the direction transverse to the axis of rotation. Therefore, this embodiment also contributes to the prevention of rust creepage and to tolerance of differences in material expansion due to heating.
A centering device for guiding the magnet wheel during mounting on the rotating element is especially preferred in accordance with the invention.
Finally, the invention provides that the rotating element is a brake disk. In other words, in accordance with this embodiment of the invention, the magnet wheel is mounted on the brake disk. In this way, the information acquired with the magnet wheel regarding the current angle of rotation and the current rotational speed of the brake disk and thus the wheel is especially accurate.